The Influence of the Residual Mg Content in the Ductile Cast Iron on the Formation Law of Spherodial Graphite

The residual Mg content ,spherodize ratio and nuclei of spherodial graphites(abbreviated SG) were studied by casting a series of similar composition ductile iron rods and white samples with different holding time of spheroidizing. The results indicate that the residual Mg content in the ductile iron was less and less as the holding time grows ,which causing the morphology of graphites transfer from spherodial to oval. Spherodize ratio change law is not continuous as increasing the residual Mg content which is divided at the 0.02%. The morphologies of nuclei of SGs core are typical examples of the highly magnified structure of spherical and irregular polygons; the diameters are about 0.5~2μm, consisting of (Mg, Ca)S along with CeO 2 and MgO. Disregistry δ between the nucleus compounds and graphite are low,which indicates that nucleus compounds are good nucleating site for SGs.The Mg element in nuclei of SG just act as nucleation substrates.it is the Mg which maybe simple substance in the metallic matrix that act as the role of spherodizer determines the graphite shape.